Let's start with a simple list. Since the beginning of 2017, there have been 187 batters to step to the plate at least 600 times, or about six per team. If we were to sort those hitters by slugging percentage, you'd get the names you'd expect. Baseball's most feared sluggers are at the top. Jose Peraza and Billy Hamilton are at the bottom.
It's a truly impressive list. You don't get to be on here by accident; you have to earn your way atop the slugging percentage leaderboard. Let's lay out the top 15, and you'll notice 14 well-respected sluggers … and one extreme surprise.
Best slugging percentage in 2017-18, minimum 600 plate appearances

1. J.D. Martinez, .676
   
2. Michael Trout, .646
   
3. Aaron Judge, .616
   
4. Jose Ramirez, .594
   
5. Giancarlo Stanton, .591
   
6. Nolan Arenado, .585
   
7. Charlie Blackmon, .579
   
8. Bryce Harper, .573
   
9. Freddie Freeman, .569
   
10. (tie) Scooter Gennett, .544
    
11. (tie) Jose Abreu, .544
    
12. Ryan Zimmerman, .543
    
13. Joey Votto, .539
    
14. (tie) Kristopher Bryant, .531
    
15. (tie) Eric Thames, .531
    Look at all those sluggers! Look at all those Most Valuable Player Award winners, record-setting home run heroes and residents of Coors Field. Look, also, at No. 10.
    10. Gennett, .544
    That's right, Gennett, who was claimed on waivers from Milwaukee barely over a year ago, who hit all of .279/.318/.420 in parts of four years with the Brewers, who is listed at just 5-foot-10 and 185 pounds, has hit like an elite slugger over the past two seasons. Eleventh best of 187 is the 96th percentile. It's star-level. It's a big part of why he just won May's National League Player of the Month Award.
    Gennett has outslugged Nelson Cruz (.529) and Josh Donaldson (.525). He's bested Mookie Betts (.525), Carlos Correa (.523) and George Springer (.518). This has been going on long enough that it appears we need to think about Gennett's historic four-homer game last June a little differently. It wasn't just a freakishly good night from a player with little track record of power. It was apparently a coming-out party.

How in the world is that possible? Let's find out.
The first thing you'd think is that because Gennett's rise to power prominence coincided with his move to hitter-friendly Great American Ball Park, that this is a story about a new home field. That's not really the case, though. While Gennett has indeed smashed at home as a member of the Reds (.311/.353/.586), he hasn't exactly struggled on the road, either (.310/.353/.509). The park may help a little with slugging, but it hasn't created the new Gennett, either -- and Milwaukee's Miller Park isn't exactly a pitcher's haven in the first place.
To hear Gennett tell it, the change actually began in his final year in Milwaukee, thanks to Brewers assistant hitting coach Jason Lane, who played in parts of seven Major League seasons for the Astros and Padres. Lane encouraged Gennett in a 2016 batting cage session to change where his back foot landed on his swing, falling behind him (towards the backstop) rather than directly under him. This would have the effect of adding some elevation to a previously flat swing.
"OK, that's kind of odd," Gennett recalled this spring in a conversation with MLB Network's Eric Byrnes about Lane's suggestion, "but I'll try it out. First swing i went, 'Boom,' OK, that felt a little weird. I did it again, and all of a sudden i'm getting true flight on the ball, because my front side is actually staying closed, I'm hitting behind -- boom -- and I've just rolled with that."

Gennett didn't actually have a great 2016, hitting .263/.317/.412, but it was a step up from his .264/.294/.381 season in '15. Still, if you looked a little deeper, you could see the changes beginning. From '15 to '16, Gennett hit fewer grounders (45.5 percent to 43.8 percent). He struck out more, but he walked more, too. Gennett's exit velocity increased as well, up from 84.5 mph to 86.7 mph.
That was just the beginning. Once Gennett got to Cincinnati in 2017, the small changes became big changes. The grounder rate continued to drop; so did his chase rate. His hard-hit rate (balls hit at 95 mph of exit velocity or more) skyrocketed to 35.5 percent, which in '17 was as good as Francisco Lindor or Javier Baez.

This year, that hard-hit rate is up again to 39.2 percent, and while that's not exactly elite -- Gennett is never going to be a Joey Gallo or Matt Olson type, up above 50 percent -- it's above average, and the same or better than more noted sluggers Eric Hosmer, Correa and Bryant.
It's important to realize what Gennett was actually saying about his work with Lane. He never said anything about "launch angle" or elevating or any metrics at all, but the effect was basically the same. By getting his bat more on plane with the angle of the pitch, Gennett has more room to square the ball up, hard and in the air. This is the way hitters work to improve, from the big obvious names like Justin Turner and Daniel Murphy to the quieter stories like Daniel Robertson of the Rays and the D-backs' Daniel Descalso.
It's probably not fair to use the four-homer game as a breaking point, because Gennett was off to a decent (though not stellar) start in the two months before that, hitting .270/.308/.450. But with Wednesday being the one-year anniversary of the feat, it's a good time to look at the hitting leaderboards since then.
Gennett has hit .318/.362/.562 in that span, which on a park-adjusted basis means he's been a Top 10 hitter. He's hit better than Harper, Blackmon or Manny Machado, and he's been doing it long enough, and with a clear enough swing change, that we can't just write it off as a hot streak. (Mostly. His .389 Batting Average on Balls in Play is the third highest in the bigs this year, and is unlikely to persist at that level. Gennett is also outperforming his expected Statcast™ metrics more than any other regular player).

Even so, Gennett just turned 28 last month, which isn't too late for a breakout. Murphy's coming-out party began near the end of his final year with the Mets, at age 30. Turner's first great year came at 29, as did Jose Bautista's. Unlikely, but not impossible. Even if Gennett doesn't continue at this level, he should at least be solidly above average for the forseeable future. (At the plate, at least; his defense at second has never been graded well.)
What this has all done, really, is give Cincinnati options. Gennett is due the remainder of his $5.7 million this year, and he has one more year of arbitration. It wouldn't be difficult to find contenders who would be interested in an offensive upgrade at second -- think the Angels, D-backs, Dodgers, Indians, Red Sox or even Gennett's old Milwaukee club, which has watched middle infielders Jonathan Villar and Orlando Arcia struggle for some time now.
Or the Reds could commit to the Cincinnati native long term if they so choose. Fourteen months ago, Gennett was a free waiver claim, expected to be a backup at best. Now, he's a nearly certain All-Star. Gennett has hit like one of baseball's best sluggers. It's a good lesson that it's not that hard to find talented players. The real challenge is helping them let their talent shine through. Fortunately for the Reds, their division rivals in Milwaukee may have helped them do just that.